1. Field of the Invention
The present invention relates to a broadband wireless communication system. More particularly, the present invention relates to a method and an apparatus for transmitting/receiving System Information (SI) including a Global Cell IDentifier (GCID) of a femto base station.
2. Description of the Related Art
In a cellular wireless communication system, a channel may deteriorate due to one or more of a geographical factor inside a cell, a distance between User Equipment (UE) and a base station, and movement of the UE, so that communication between the UE and the base station is hampered. More particularly, when a UE is located inside a closed building such as an office or a household, a channel between a base station and the UE may be deteriorated in a region referred to as a shadow region. The UE located in the shadow region has difficulty in communicating with the base station.
A pico cell concept is being proposed to provide a service to the indoor shadow region, and a femto cell concept is being proposed to provide a data service of a far higher level to even more users while addressing a service limitation of the indoor shadow region. The femto cell has a smaller coverage area then that of a macro cell. A plurality of femto cells may be installed inside one macro cell area.
As a plurality of femto cells are installed inside one macro cell area as described above, a Physical Cell IDentifier (referred to as ‘PCID’ hereinafter) which is one of identifiers identifying the femto cell may be repeatedly used inside one macro cell area. That is, since 3rd Generation Partnership Project (3GPP) and 3GPP2 standards allow for a reuse of the PCID, two or more femto cells included inside one macro cell area may have the same PCID. Therefore, the macro cell cannot identify a femto cell of a relevant cell using only a PCID of an adjacent cell reported by a UE.
Therefore, a method of allowing each femto cell to report the PCID and a Global Cell IDentifier (GCID) together is being discussed, and, a method of allowing a UE to obtain the GCID from a femto cell is being discussed.
The GCID is included in System Information (SI) that includes information of a relevant femto cell and is transmitted, and each UE receives the SI during a predefined measurement gap assigned for cell searching by a serving base station.
The conventional art provides two techniques for receiving SI from a base station of the femto cell. One is a technique of lengthening a measurement gap and increasing a probability that SI is received for the lengthened gap. However, it is difficult to use this technique when a time of suspending data transmission/reception is not as long as in a Voice over Internet Protocol (VoIP).
The other is a technique of requesting and receiving a separate measurement gap pattern from a base station of a macro cell in order to search for the base station of the femto cell. For this purpose, a signaling message exchange as illustrated in FIG. 1 is used.
FIG. 1 is a view illustrating a signal flow for reception of SI in a conventional broadband wireless communication system. Referring to FIG. 1, in step 110, UE 100 determines if a measurement gap pattern for receiving SI is needed. In step 112, the UE 100 requests a macro base station (macro eNB) 104 to transmit the measurement gap pattern. In step 114, the macro base station 104 generates the measurement gap pattern for the SI using information of a relevant femto base station, and in step 116, transmits the generated measurement gap pattern to the UE 100. In step 118, the UE 100 searches for neighboring femto base stations during the measurement gap. In step 120, the UE 100 enters a region of a femto base station (femto eNB) 102 identified during the search. In step 122, the UE 100 receives SI transmitted from the femto base station 102 during the measurement gap.
As described above, the technique of being assigned the measurement gap pattern requires a signaling exchange between a macro base station and UE. When the macro base station does not have information for a relevant femto base station, the technique additionally requires a signaling exchange (210) between a macro base station (macro eNB) 202 and the relevant femto base station (femto eNB) 200 as illustrated in FIG. 2. FIG. 2 is a detailed view illustrating a signal flow for reception of SI in a conventional broadband wireless communication system. That is, since the technique of being assigned the measurement gap pattern requires signaling between the macro base station and the femto base station in addition to signaling between the UE and the macro base station, an additional delay may occur during a handover.
Therefore, there is a need for a new technique which may receive SI even when there is a short amount of time for suspending transmission/reception, and which does not require a complicated signaling message exchange.